The present invention relates to knock control apparatus for internal combustion engines, and, more particularly, to a knock control apparatus for controlling an occurrence of knock during the acceleration of an engine.
Engine knock may cause a melting of the pistons or the exhaust valves and other damage to an internal combustion engine. Thus, with the conventional ignition systems for engines, to prevent the occurrence of serious troubles due to knocking, an ignition timing control method has been proposed which establishes a retarded actual ignition timing. The knocking in the engine causes, in addition to knocking sound, a reverse torque which decreases the power output of the engine or an overheating of the engine. There is a close relationship between the knocking and, the ignition timing and from the engine characteristic point of view, the maximum power output of the engine can be obtained by setting the actual ignition timing or the ignition advance angle at a point just before prior to the point at that which a knocking occurs. As a result, to greatly retard the ignition timing or to decrease the ignition advance angle so as prevent the occurrence of knocking has the converse effect of decreasing the engine output and there is a need to control the ignition timing at a point just prior to the occurrence of knocking.
A known knock control apparatus removes an ignition-induced ignition noise by masking the noise from the output signal of a knock sensor to detect a knock signal and the ignition timing is retarded a predetermined angle in accordance with the detected knock signal. In other words, the ignition timing is retarded a predetermined angle of, for example, 4.degree., in response to the knock during the interval between the adjacent two ignition timings. More specifically, whether the ignition timing is to be retarded is determined in dependence upon the presence or absence of a knock signal and the ignition timing is retarded a predetermined angle in a stepwise manner (a so-called stepping retard method) in response to the detection of every knocking condition.
Generally, during the period of acceleration from an idling condition of the engine, the frequency knocking is high and there is a greater tendency for heavy knocking to continuously occur. With the known knock control apparatus, however, when the engine knocks, the knocking is eliminated by retarding the ignition timing of the engine a predetermined amount irrespective of the engine operating range or the engine speed. Consequently, if the amount of retard of the ignition timing for the engine is set to a value suitable to prevent the occurrence of knocking at the low engine speeds, the ignition timing characteristics for preventing the occurrence of knocking at the intermediate and high engine speeds is unsatisfactory and it is impossible to ensure satisfactory engine performance. Thus, it is the general practice to set the amount of retard upon occurrence of knocking to a value suitable for preventing the occurrence of knocking at the intermediate and high engine speeds.
As a result, when knocking occurs, the ignition timing is retarded a predetermined number of degrees and controlled at a value which eliminates the knocking. In other words, the ignition timing is retarded a predetermined number of degrees in response to every knocking condition and the retardation of the ignition timing is continued until the knocking is eliminated. The ignition timing at which the knocking is eliminated does not necessarily represent the optimum ignition position and thereafter the electronic advance function again comes into action thereby advancing the ignition timing in the conventional manner.
However, this type of known method is disadvantageous in that during the acceleration of an engine where knocking occurs continuously, the amount of ignition timing retard per knocking condition becomes insufficient thereby deteriorating the control response to the knocking and considerably degrading the running performance. A primary object of the present invention resides in providing a knock control apparatus for internal combustion engines capable of preventing the occurrence of heavy knocking during the acceleration of an engine.
To accomplish the above object, in accordance with the invention, means are provided for detecting the acceleration condition of an engine so that, upon detection of the acceleration condition, the amount of retard of ignition timing provided upon occurrence of knocking is increased as compared with that provided during the steady state operating condition of the engine, that is, an operating condition other than the acceleration condition.